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Could I receive flight training in my company's jet, while on company business with passengers?
On occasion I will travel on my company's corporate jet. From a legal/FAA standpoint, are there any regulations against receiving flight training from a CFI with the proper ratings and currency during those flights? I'm a private ASEL pilot, so this would be working on an instrument/multiengine/type rating. And does the answer change if the jet is certified for a single crew member vs requiring 2 pilots? Assume that my employer is ok with this if it's legal.

Depends, is the plane on company business with passengers?

It would be, yes. I know I can't act as PIC since my PPL isn't multiengine, so that shouldn't matter for part 61.113. They always have 2 pilots (who are both CFII multi) when taking out the plane.

I suspect the next pertinent bit of information is whether your company operates under part 91 or part 135. Either way, I'm interested in learning the answer to this question! Welcome to Aviation.SE!

If it is certified for more than one crewmember, then you would need to meet the requirements of 61.55 in order to be a required crewmember (SIC), and that includes having your multi-engine rating and an instrument rating if flying IFR so no.

It is an interesting question and needs quite a few FAR's to figure out. Let's start with having other people on board:
If the aircraft is not certified for single-pilot operations, then you cannot based on FAR 61.89(b)

(b) A student pilot may not act as a required pilot flight crewmember on any aircraft for which more than one pilot is required by the type certificate of the aircraft or regulations under which the flight is conducted, except when receiving flight training from an authorized instructor on board an airship, and no person other than a required flight crewmember is carried on the aircraft.

If it is certified for single-pilot operations, you may be able to receive training as long as you are not PIC and you are not sitting in the left seat (as almost all single-pilot jets that are certified single-pilot usually have a restriction to left seat only).
However the real rub comes in when you consider that you are a private pilot, not a commercial pilot, and the FAA's extremely broad definition of "compensation". On more than one occasion, the FAA has held (and won in court) that getting flight time in furtherance of a certificate is compensation. Technically just receiving your normal compensation (hourly wages) is enough to meet the definition of being compensated for flying.
The only way to get a real good answer to this, because it is a very broad subject and open to legal interpretation, is to engage your local FSDO.
I'm guessing though that the ultimate answer will be no. Aside from the issues with the FAA and FAR's depending on what operations your employer is conducting under (121, 135, 91, etc), your employer will also have to consider aircraft insurance. Many corporate jets are insured only for certain pilots or pilots who meet minimum qualifications and the insurance policy may completely bar primary training of any kind in the aircraft.
So talk to your FSDO, if you get an OK from them, the next step is to talk to the corporate attorney or an aviation lawyer and have them review the insurance documentation to see if you are allowed to sit in one of the seats and manipulate the controls.

Thanks for the detailed response. It's interested that I could (potentially) be considered a student pilot under 61.89(b), but then you note that I'm private and have the compensation/for-hire limitation.

Now this all becomes an academic discussion moving forward since our jet isn't certified for single-pilot operations and I'm not high enough in the company to take it without other passengers. But I'm still curious to solve it :)

I'm not sure your 61.89 interpretation is completely accurate. The OP isn't a student pilot, so it wouldn't apply to him. And the wording says that a student pilot can only be a required crewmember on an airship that isn't carrying passengers, so an airplane is out of the question anyway, whether or not there are passengers on board. At least, that's my reading of it.

@Pondlife I guess that is why aviation attorneys make so much money. I read it as a pilot under instruction (aka student pilot) because I believe that just about any pilot training in a jet or commercial aircraft is at least a private pilot, most likely having obtained a commercial certificate in GA aircraft long before they sit in something like a jet. I believe any pilot under instruction in obtaining a new rating or certificate is considered a student pilot when exercising student privileges of the certificate they are trying to obtain.

Good point about the attorneys :-) But AFAIK a "student pilot" is a pilot who holds a student pilot certificate, not a pilot who's in training. 61.89 is part of subpart C, and you can see that 61.81 says it "prescribes [...] the general operating rules and limitations for the holders of those certificates". Once you get a private certificate you no longer hold a  student one and you're never a "student pilot" again in the FAA's eyes, you're just a pilot training for a new rating or whatever.


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Do we need to do the SELCAL check if given an HF frequency by datalink?
If the controller sent us a message through datalink to monitor HF frequency (P xxxx S xxxxx ) and continue CPDLC, do we need to do the SELCAL check?

Is the HF frequency your currently assigned frequency or is it a new one?

A NEW ONE. USE VHF CURRENTLY.

Then yes, you are required to either do a SELCAL check or continuously monitor the frequency. I didn't have time to write up a full answer with references though!

@Lnafziger pls write in detail, i need to check the references

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Why does centre of pressure (drag?) move forward when transitioning from transonic to supersonic?
I am studying aerospace engineering at college and I am wondering why the centre of pressure moves forward when the aircraft changes from transonic flight to supersonic flight?
Also, is centre of pressure the same as centre of drag? I can't find anything on centre of drag but I've found loads on centre of pressure.

I'm certain the question of why CP moves has been answered somewhere but I can't find what question it's on. My Google-fu is off today. There's some info on this answer and this one. I've never heard anyone use the phrase "center of drag" before. I guess there would be one, but it wouldn't be the same as CP. The induced drag probably acts at the same point, but I'll let somebody that knows what they're talking about answer that. Peter Kämpf will prob be along before too long :)

The center of pressure does not move forward when transitioning into supersonic flight, but back. Let me compare the pressure distribution around a sub- and a supersonic airfoil, and the reason should be obvious:
First subsonic flow, showing an Eppler 502 at a moderate angle of attack (3°):

And here is a rhombic airfoil in supersonic flow, copied from this answer:

While the pressure difference between upper and lower side is highest near the leading edge in subsonic flow and tapers off the more you move backward, the pressure difference between both sides is constant over chord in case of the supersonic airfoil. An uncambered rhombic airfoil is the simplest case: The pressure jumps up when the air passes through a shock and jumps down when it passes trough an expansion fan. In between, pressure is constant because the local inclination of the surface does not change.
As a consequence, the center of pressure is near the quarter point in subsonic flow and at mid-chord in supersonic flow (when tip effects are neglected).
Even in transsonic flight, when the local supersonic flow delays the pressure rise, the center of pressure starts to move back. This is the reason for the pitch-down experienced when accelerating above the critical Mach number which is called Mach tuck.
OK, now I forgot to mention the center of drag so far. It is of minor importance because the drag force is so much smaller than the lift force. The concept is the same: Sum up all drag contributions and find the point where a discrete force applied in the direction of drag has the same effect. While the center of pressure just sums up all pressure (and includes the portions which contribute to drag), the center of drag mixes both shear and pressure effects and looks at the fraction which acts in flow direction.

When transitioning from transonic to supersonic flight, the Center of Pressure (C.P.) actually moves rearward.
As the airfoil moves through the air and enters transonic speeds, shockwaves starts to form; which causes an increase in pressure on the shockwave region. This increase in pressure contributes to where the center of pressure (C.P.) concentrates.
Now as the airfoil goes faster (towards supersonic), it'll leave the shockwave behind, thus, moving the C.P. towards the rear.

The Centre of Pressure is the point at which the lift acts on the wings of an aircraft (think about it as putting pressure on the wings to move it up)
The Centre of Gravity is the opposite, it is the point at which gravity acts on the body of an aircraft pulling it down. If you have a nose-heavy aircraft, then your Centre of Pressure is behind your Centre of Gravity (pushing the nose down and the tail up)
I have not heard of the Centre of Drag, but don't just assume that it's the Centre of Pressure as the Centre of Pressure relates to lift, not drag.

The center of pressure is not the same as the lift vector. There is a component pointing toward the tail caused by drag.

You defined the terms, but you didn't answer the question.

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What materials are suitable for making a mini gas turbine engine?
What materials are suitable for a mini/model gas turbine engine, specifically the fan, compressor, combustion chamber and turbine?

Could you share the result of your current search? Related: What material is used to make the hot sections of jet engines? and What is the material composition of aircraft compressor blades?

it really depends on your requirement. if you don't care about anything you can make everything out of steel and it will work, and may work very well for certain applications. choice of material depends on mostly cost, weight, strength, and temperature. Hot sections like turbine mostly take temperature and strength and don't care cost and weight, uses nickel-based alloy . Not-very-hot compressors takes temperature weight and strength and don't care cost either, so titanium is popular. Fan is not hot at all can get expensive and heavy because it's large so aluminum and titanium are both common.

Materials are one thing. You also need tools and machinery to build one: the turbine and compressor in a mini jet engine rotate at ~100,000 rpm so they're subject to significant stress. They have to be balanced perfectly.
If you want to build one yourself, look into using a turbocharger from a car engine as the core. That gives a decent base for the high-temperature parts of the engine. Others have built DIY jet engines from turbochargers.

GE took on this very task and was able to successfully 3D print a working a working get engine scaled for a model sized aircraft. Although they only claim to use "high strength alloys" and are presumably not going to let the world know what its actually made of. There are lots of easily available small jets for RC planes you may want to look into. There is a nice article here about an engine that utilizes a steel combustion chamber and ceramic blades. You could make one successfully out a variety of materials depending on what you are trying to do.

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Is it possible to have dual contra-rotating rotors on a gyrocopter or gyroplane? Are there disadvantages that would outweigh the extra lift?
Is it possible to have dual contra-rotating fixed-pitch rotors on a gyrocopter or gyroplane?
It would seem to me that it would provide a lot more lift.  I am wondering if any disadvantages would outweigh the extra lift?

If you have fixed pitch rotors you won't be able to maneuver the craft.

@Carlo Felicione  Most present-day gyros are fitted with a two-blade semi-rigid rotor, fixed pitch. The inclination of the rotor head can be controlled with the stick, so you can freely tilt the rotor plane, the thrust vector thus changes direction, and the machine follows...

Because gyro rotors do not impart any significant torque on the fuselage you don't need the rotors to be contra-rotating. Biplane rotors that rotate in the same direction would work just as well.

@slebetman wouldn't contra-rotating rotors (contra-rotors..?) help solve the problem of the retreating blade stalling at higher speeds?

You can get additional lift with a larger rotor, without going to the extra complication of having two of them. Present-day autogyros are very light machines that have more than enough with one rotor. Besides, in the case of the coaxial configuration, the centre of mass of the machine will be much higher, a very undesirable thing for landings, as any gyro pilot would attest...

I've long thought that a dual-rotor gyroplane, where the rotors are mounted side-by-side with a "coordination shaft" between them (such that they mesh) would be a good idea.  Look at the Flettner and Kaman  helicopters for examples.
It's true that gyroplanes don't need a tail rotor or multiple rotors to offset rotor torque because, since the rotor is flying in autorotation, there is little / no rotor torque to offset.  There is, however, a problem with speed.  And it's a problem which helicopters also have to wrestle with: retreating blade stall.
As your forward speed increases, the rotor produces more and more lift on the "advancing" side of the rotor disk but it produces less and less lift on the "retreating" side because the forward airspeed of the retreating rotor blade approaches 0.  Many, modern helicopters actually reduce the pitch on the advancing side, to keep the lift from getting asymmetric, and limit forward speed.  If you watch some videos of gyroplanes, especially ones which are really hauling, you'll note that the rotor disk isn't horizontal; in fact, some of them are pretty steeply "rolled," indicating very asymmetric lift on the rotor.  At least one of the designs out there has the landing gear legs designed such that the one on the advancing side of the rotor is neutral on lift, but the one on the retreating side actually provides lift to help offset the asymmetric lift from the rotor.
One of Sikorsky's later designs uses a co-axial rotor (one above the other on the same mast, rotating in opposite directions).  This way, as one rotor's advancing side is the other rotor's retreating side.  The rotors may provide asymmetric lift but the combination of the rotors provides symmetric lift, even at higher speeds.  The Russian Kamov design bureau has been doing this for decades.
The CarterCopter has small wings.  It uses the rotor for takeoff and low-speed flight.  As speed increases, the wings "take over" on lift and the rotor pitch changes to produce less lift, such that it can fly even if the retreating side has zero airspeed.
With meshing rotors, you could put the advancing side of the rotor disks outboard and the retreating side inboard, such that the two rotors would maintain symmetric lift as speed went up.  And since the rotors would be be retreating as they spun over the fuselage, it wouldn't really matter if they produced zero lift during that part of their travel.
I would think this would a VERY GOOD idea.  But I know of no instances where anyone has actually done such a thing.

Flapping indeed takes care of asymmetric lift, which only poses a problem at high speed. Gyrocopters are used here in Australia for cattle mustering, by farmers who use them as airborne motorcycles. They have no requirement for a complicated rotor arrangement.

Look at rc twin rotor gyros. They perform quite well. Instead of having articulated blades they are fixed and counter rotating at the end of opposing booms .The rotors are shorter and spin much faster on ground roll for takeoff. However I would make the rotors tilt fore and aft independently for pitch and roll control and use more ruder to coordinate turns. I believe this would work better than an elevator controll surface. A faster prerotation could be attained with a motorcycle starter motor at each rotor. The shorter blades won't require as much torque to get to takeoff speed . That means a shorter ground roll. The only drawback I can think of is having to make more blades .

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How efficient is a Scramjet?
I searched about the subject, but I couldn't find any place where the overall efficiency of the scramjet is compared to the other types of engines.
All they say is how the "Scramjet is more efficient than rockets inside atmosphere" and how they are "better than ramjets", but they lack the numbers for these claims.

A scramjet is more efficient than a rocket engine for the same two reasons that all air-breathing engines are more efficient than (chemical) rocket engines:

Chemical rocket engines need to carry both their own oxidizer and their own fuel, whereas air-breathing engines only need to carry their fuel and take the oxidizer from the air. Therefore, for the same mass / volume, they can carry roughly twice the amount of energy, or for the same required energy, they need to carry roughly half the amount of propellant. (It's not exactly 2:1, of course, because of different densities and stoichiometric ratios.)
Rocket engines need to carry all their reaction mass with them, whereas air-breathing engines simply suck in reaction mass at the front and throw it out again at the back. This means that

For rocket engines, the reaction mass is finite, for air-breathing engines, the reaction mass is infinite.
For rocket engines, the reaction mass eats into the payload capacity, for air-breathing engines, it is "free".

These points are true for all air-breathing engines, not just scramjets. Air-breathing engines, in general, are more efficient than chemical rocket engines: ramjets, scramjets, turbojets, turbofans, turboprops, all of them.
Note: I only consider chemical rocket engines here, not nuclear-thermal, nuclear-fission, or nuclear-fusion ones.
As for the comparison between ramjet and scramjet, it is actually not true that scramjets are more efficient that ramjets, as a blanket statement. It depends on the speed:

Below Mach 4, scramjets don't even work, so talking about their efficiency makes no sense.
Between Mach 4 and Mach 5, ramjets are more efficient than scramjets.
Between Mach 5 and Mach 9, scramjets are more efficient than ramjets.
Above Mach 9, ramjets no longer work, so talking about their efficiency makes no sense.

(All numbers rough approximations.)
See the $I_{sp}$ graph from the accepted answer to the related question Is the compressor required on jet engines? Can air be rammed into the turbine? for details:

Scramjets use super compressed air from the atmosphere, while a rocket engine carries its own oxidiser. This main difference means that all weight and volume required for the oxidiser and reaction mass in a rocket, can be used for fuel only in a scramjet. So all being equal, the range of the scramjet is larger than that of a rocket.
But all is not equal: scramjets can only operate at speeds far exceeding Mach 5, while a rocket engine thrust is instantaneous. Provide enough volume, and the range is all the way to the moon, without requiring any oxygen at all.
And this is the main difference, not so much the increase in efficiency described in this answer. The scramjet flies superfast in the atmosphere, and can therefore use conventional flight controls to control the trajectory - it is basically a cruise missile.

Also, rockets need to carry all their reaction mass, whereas air-breathing engines have infinite reaction mass for free.

@Koyovis: Both reaction mass and oxidizer.

@Koyovis I don't think those are equivalent; consider nitrogen from the atmosphere; it is expelled from the exhaust at a greater speed than it was consumed at the intake, providing thrust, counting as reaction mass. It is not, however, an oxidiser.

ON top of what @marcelm says, the reaction mass in a typical, chemical rocket is the combustion products plus any residual unreacted material from the tanks (in the past various non-burning additives have been used, but less so now).  It's an interesting overlap of meanings:  "reaction" as in "chemical reaction" (or simply "burning" here) and "reaction" as in "action and reaction are equal and opposite"

Scramjet has the advantages of simple structure, light weight, low cost Unit thrust (thrust generated by propellant per unit mass flow) high and fast. Compared with rocket engine, scramjet does not need to carry oxidant. Therefore, it has a larger payload and is suitable for the power of hypersonic cruise missile, hypersonic aircraft, transatmospheric aircraft, reusable space launcher and single-stage orbit space aircraft. Due to its important Scramjet has attracted much attention all over the world.


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Is there any regulation to ensure that life jackets and safety cards are on-board?
On many flights, I was told that a life jacket is under my seat and safety card is in the pocket in front. Is there any regulation that ensures that life jackets and safety cards are on-board on all flights?

My meaning is passenger can easily takes life jacket off airplane. What is done to make sure next passenger has these safety stuff on next flight?

Interestingly enough: For US Airways 1549 (2009 Hudson diching), 70% of the passengers did not watch the safety briefing and more than 90% did not read the safety information card. Despite the fact that the flight was flying over the land and life vests were not mandatory, it was equipped for extended water operations. However only 33 passengers out of 150 got their life vest with them when leaving the cabin, and only 4 completed its donning, as visible on the famous image.

@mins: That image is no longer in that location.

@Sean: Thanks, this is the picture of the aircraft floating with passengers on the wings.

The FAA has a similar requirement (commercially under part 121)

(a) Except as provided in paragraph (b) of this section, no person may
  operate an airplane in any overwater operation unless it is equipped
  with life preservers in accordance with §121.339(a)(1) or with an
  approved flotation means for each occupant. This means must be within
  easy reach of each seated occupant and must be readily removable from
  the airplane.
(b) Upon application by the air carrier or commercial operator, the
  Administrator may approve the operation of an airplane over water
  without the life preservers or flotation means required by paragraph
  (a) of this section, if the air carrier or commercial operator shows
  that the water over which the airplane is to be operated is not of
  such size and depth that life preservers or flotation means would be
  required for the survival of its occupants in the event the flight
  terminates in that water.

In other words they are only actually required (per FAA regulations) when operating over water so not every plane (route provided) technically needs them. However many airplane seat bottoms may double as a personal flotation device so many planes are equipped with them by the nature of their construction.

And the briefing cards?

User11933, has reproduce the legislation refering to those specific items.To answer your other question ie:who checks it.The flight attends do, in theory. After each flight they are supposed to check and make sure none is missing.It is part of the equipment of the aircraft and as such, listed in the MEL.(Minimum equipment list) which is the document listing all the systems and equipment mandadory on board.
Obviously the captain is ultimately responsible. On smaller aircrafts with no FA, it is actually up to him or to the FO by delegation, to make sure they are on board before departure.
Hope that clears it up :-)

Do you have a reference for any of that? I see flight attendants checking various emergency equipment regularly, but life jackets & safety cards, not so much. While a missing life vest CAN be deferred using the MEL, I've never heard of the safety demo cards being deferrable that way.

I was refering more to the life jacket as far as the MEL is concerned, not so much the safety cards. References would come on the OM(Operators Manual) who implements it the way he thinks appropriate.


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How is the ALSF-II approach lighting system built and powered?
The ALSF-II approach lighting system includes lead-in groups, a decision bar, red side bars and sequenced strobes:

ALSF-II approach lights for KRFD - Chicago-Rockford Intl (source).
Does anyone know the number and type of lights used, how they are arranged (distance and slope) and how much power is required to feed the full system?

The specifications for an ALSF-2 (and other approach lighting systems) can be found in FAA JO 6850.2B - Conveniently titled "Visual Guidance Lighting Systems."
As an FAA order these are obviously US-specific, but other jurisdictions' guidance is probably similar.
The ALSF-2 is a High Intensity lighting system, so lights used in the system are defined in the FAA order as follows:

High Intensity Systems.

Specification FAA-E-2408b, 300-watt, 20A, PAR-56 lamps for steady-burning, aboveground, white lights with Specification FAA-E-982 lampholder.
Specification FAA-E-2408b, 500-watt, 20A, PAR-56 lamps for steady-burning, aboveground, colored lights with Specification FAA-E-982 lampholder.
Specifications FAA-E-2952 or FAA-E-2491 approach lights, 500-watt, for all semiflush lights.
Specifications FAA-E-2628b or FAA-E-2689a for all sequenced flashers.

From the number of required lights we can then derive the total system power used for an FAA-Specified ALSF-2 lighting system -- As I'm not fond of doing math it's fortunate that some manufacturers have already done this for us, and a full system (with all the flashers) requires approximately 104kW (varying slightly depending on input voltage). Actual utility power consumption will vary based on the efficiency of certain components but will likely shake out to something around 104kVA since the incandescent lamps have a power factor close to 1.0.

@mins You are correct - I misread the sheet, and that's apparently the power for the flashers only (which makes a lot more sense if they're using incandescent lamps). Adding your number to that number and assuming a power factor of 1 gives a little over 100kVA for the whole system, which does seem much more reasonable with incandescent lights!

I thought about this figure being the flashers power only too, but was confused by the non-linearity when the number of flashers increases (page C-8). But now my second thought is it could be because energy is stored in a capacity (BTW a flash tube can deliver 100 μs pulses, not an incandescent filament), discharged at interval and they improve time efficiency (duty cycle) in parallel with power supplied.

@mins Yeah, the flashers have an efficiency less than 1.0 because of the reactance in the circuit (we have to rectify to DC and charge capacitors, or step up the AC in a coil to spark the strobe). Considerable power savings could be had by converting the whole mess to LEDs, but as far as I know that's not formalized in a standard/technical order yet


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How does a vertically higher center of gravity affect handling?
Much of the discussion of the center of gravity of the aircraft is focused on the longitudinal axis, i.e. front and back. How does the vertical position of the CG affects the handling characteristics?
For example, the Boeing Dreamlifter and the Airbus A300-600ST both have their cargo stored in the upper portion of the airframe. Are these aircraft easier to "flip over"?

Related

On ground or in the air?

@vasin1987 in the air.

As long as flight is coordinated, the vertical position of the center of gravity (cg) is of minor importance. It will show in issues like thrust changes, when acceleration will cause higher trim changes because of the increased lever arm between the inertial forces and the thrust forces.
This will only change when flight is no longer coordinated and the aircraft sideslips. Now the big cargo volume is more important than the cg location because it will contribute a considerable side force. Also, it will need additional means of lateral stabilisation because the big fairing will destabilise the aircraft in yaw. Still, the lever arm between the cg and the lift force vector will be much, much smaller than the lever arm of the ailerons, and a little aileron deflection will be enough to stabilise the aircraft.
Maneuvering will look funny to crews used to fly the unmodified version of the same airplane, because now a roll manoeuver will induce a lateral motion at the location of the cockpit which was not there before. Same goes for eigenmodes like the Dutch roll which will be more noticeable for the crew because their cockpit sways laterally.
"Flipping over" needs deliberate commands from the pilot; this is no different in aircraft with unusual vertical cg positions. The most extreme is probably the VM-T "Atlant" version of the Russian M-4 Molot bomber.

M-4 Molot version VM-T Atlant with Buran booster tank (picture source)

Most airplane designs take advantage of the CG vertical offset wrt the center of lift to help auto pitch the plane with overall configuration of wings and elevators and engine's thrust.
You get auto pitch up when you add to thrust of engines and vice versa you get nose down by reducing power. Im emergencies this is the only last resort of controlling the pitch.
An easy way of imagining this is to think of the plane as hanging from a long string: add more power it pitches up; reduce power it pitches down.
Each plane design has a manufacturer's design volume inside which CG will create acceptable moment arm to safely control the plane and fly it. Many crashes have happened because of violating this limitation. In Cargo planes there are loading charts and anchors prescribing where and how to lock in tall loads or how to distribute loads in cargo space.
Handling of a plane with higher CG requires more carful control of coordinated flight to prevent potential wild banks or stall of one wing in turns.

Most of the content in this answer (except the last paragraph) does not answer the question.


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Why does the B777 have no winglets? Are there any drawbacks to having winglets?
I have googled and noticed that almost every Boeing 777 is not equipped with winglets. Does anybody know the reasons why Boeing did not equip B777s with winglets? Are there any drawbacks to having winglets?

Winglets are usually an afterthought. The 777 wing was design with a modern understanding of aerodynamics.

As in anything in aviation design, the use of wingtips has both advantages and disadvantages. In the end, the decision to use (or not) a winglet is based on the cost-benefit analysis of the winglet to be used in that particular aircraft.

All winglets incur a drag and weight penalty- the question is whether they conserve fuel more than they increase it in the first place.
One problem in winglet addition is that they are prone to flutter.
Also, an equal span extension is sometimes more effective and is less risky.
Another thing to add is that most of the present aircraft using winglets (A320s and B737s) were not designed with winglets to begin with. They were retrofits. Most of the new aircraft are designed with plenty of aerodynamic experience and the engineers can take a call based on the data available as to whether to have 'conventional' winglet or not (See A350XWB Vs B787).

Coming to B777, it should be noted that the -300ER, -200LR, and -200F have wingtip devices after all- raked wingtips. These act in the same manner as the winglets to reduce drag.

Boeing 777 raked wingtip; image from Boeing.com
According to Boeing,

Each wing on the Boeing 777-300ER (extended range) is being extended by 6.5 feet, and raked wingtips are being added to improve the overall aerodynamic efficiency. The raked wingtips help reduce takeoff field length, increase climb performance and reduce fuel burn.

So basically, these act in the same manner as the conventional wingtips. Also, it is crucial to consider the tradeoff. B777 was designed when the advantages of the wingtips were well known, yet they decided to go without one anyway. From airspacemag:

Because winglets are a tradeoff: In the highly visible case of the 777, an airplane with exceptionally long range, the wings grew so long that folding wingtips were offered to get into tight airport gates.

Finally nobody ordered the folding wingtips when they were first offered, though that has not stopped Boeing from trying. Note that one main reason for offering folding wings is to fit into existing gates- else the wingspan would've become too great.
Boeing considered all the options before deciding to go with this option:

Dave Akiyama, manager of aerodynamics engineering in Boeing product development, points out that designing winglets can be tricky-they have a tendency to flutter, for example. "We find that it really doesn't matter what kind of wingtip device you use-they're all like span," he says. "The devil is in the details. Span extensions are the easiest and least risky."

And finally, winglets were considered for B777, especially for the earlier versions, though nothing came out of that- so most probably they were of not much use in improving fuel burn. Note that 787 also has a similar 'raked' wingtip instead of winglet.
Note: The fuel burn can be reduced by other means than wingtip devices- Boeing did exactly the same through Performance Improvement Package (PIP) for the Boeing 777, improving fuel burn by 1%:

... for long-range 777s, with United, Continental, and Delta investing in
  modifying the outboard aileron droop and the environmental control system, making ram air improvements, and installing smaller wing vortex generators to yield a total of 1 percent fuel burn improvement.

That is very kind of you. Many thanks to your crystal-clear answer.

747-8 is also a well-known user of raked-wingtips

Only the 300ER and the 200LR have the raked wingtips.

One thing I'd add to this: when the 777 was released, it had an unusually long wingspan compared to most aircraft in service. Since then, the number of 777, 747, A380 and other long wingspan aircraft has meant there are plenty more gates available to handle the increased wingspan

Another potential drawback to winglets is that of gate spacing at the ramp. Winglets can make for a much larger footprint at the gate. This could, in turn, make 5 airplanes without winglets into 2-3 planes with winglets, depending on spacing requirements and availability.
You might be saving on gas for long haul routes, but if you’re only hauling 50% of your passengers and/or freight because you can’t stuff enough airplanes into “Airport X,” then you’re not really saving on much in the first place.

It seems you are confusing winglets (vertical extension) with wingtips (horizontal extension), as winglets do not add much to the width of a plane. Also you are answering a question thats over a year old.

No confusion. In order for winglets to go up, they have to go out as well. On the 757, for example, it was drastic enough (13 feet of extra clearance on each side, if memory serves) for my operator to opt out of winglets entirely as it would have required an extraordinary amount of extra gates. I don’t remember the exact number, but I believe it was something like 20 fewer overall aircraft. The difference between lost lift vs. fuel savings on short routes wouldn’t have added up. So, yes, it is a significant factor. Sorry for the thread necromancy.

Out of curiosity, was your "operator" an airline or an airport or something else? Usually an airline would be considering which aircraft to order whereas an airport would be considering how to lay out their gates. Your comment implies consideration of both by one entity which isn't something I've come across before.


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What is needed to take off in CAT IIIb weather and how is it done?
Landing is possible down to 150 ft visibility and no useful vertical visibility using CAT IIIb ILS. This relies on ILS not only for navigating to the runway, but also for maintaining runway centreline during roll out down to taxi speed.
So is it also possible to take off in such weather and if so, how is it done?
(edit) Answer to Who authorizes low visibility takeoff operations for airlines, and what is required? mentions take off is possible down to 300 ft RVR with a "takeoff guidance system". So more specifically, how does that work?

IIRC if you can't land then you also can't takeoff (to ensure you can get back to ground in case of emergency)

@ratchetfreak: That does not seem to be true, see When do I need a takeoff alternate?. And I am asking about when I can land anyway.

@JanHudec on the practical side, the takeoff is just like any other, you just see less centerline stripes / lights than normal.

@casey: I wanted to know whether there is any automation for the lowest visibility conditions. The other answer you found mentions a "takeoff guidance system", without details. So explanation what that is would be interesting.

@casey that is a related question, not a duplicate. The other question is about the legality of liw vis take off (in the USA, for flights operated under part 121). This questions is about the technical and operationale aspects and seems not to be limited to the USA.

@JanHudec with the discussion and edit the Q has become clearer and I've retracted my VTC and remove my comments.

Under the US FARs (at least part 91) nothing special is required to take off in CAT IIIb weather besides an operational (and IFR-legal) aircraft and pilot. As mentioned elsewhere you can legally make that Zero/Zero takeoff where you can't even see the runway under your nose.
It should go without saying that doing so would be incredibly stupid (we (and the FAA) have said so anyway), but from a technical standpoint there's nothing preventing the operation except the knowledge that you might run off the side of the runway into a ditch and bang up your aircraft and passengers.

In terms of what would be required to make the takeoff safely, without running off the side of the runway into a ditch, I'd posit that you would need the same capabilities as you'd need to make the CAT IIIb landing safely: Aircraft systems that let you reliably track down the centerline for takeoff (using the ILS or something of equivalent accuracy for guidance, and runway centerline lights).
You would also need a reliable way to get from the gate to the runway, so taxiway centerline lights & stop bar lights are a must, and probably ASDE-X or its functional equivalent with a controller monitoring it to help ensure you don't taxi into another aircraft.
All of the above is predicated on, among other things, being able to see the lights I mentioned. The "takeoff guidance system" mentioned elsewhere adds synthetic vision into the mix which further enhances safety (and in the airline world allows takeoffs down to 300ft RVR). From what I can glean from the Rockwell-Collins marketing material their HGS seems to be able to provide "follow the green dots" taxi guidance (and presumably runway centerline guidance for the takeoff roll as well), providing redundancy for the lights I described above to help the pilot ensure the aircraft is going where they want it to.

With all due respect, I have to disagree with your view "that doing so would be incredibly stupid." The FAA, of course, used the somewhat less abrasive language "never advisable." Even so, I have to disagree with that as well. Perhaps it's a generational thing, but I and others never considered ourselves doing something stupid when we made such takeoffs (all without incident) in everything from single engine aircraft to 747s. The scenario was usually the same, repositioning an empty aircraft under Part 91 from a socked in field to a open field relatively close by.

@Terry Actual, true 0/0 takeoffs would be incredibly stupid.  That being said, I have never seen visibility down to the point where you couldn't see at least a light or two (at night) or where you can't even see the pavement below you.  This is partially because you couldn't even make it to the runway in those conditions, so the weather is automatically better than 0/0 if you taxied to the runway in the first place.

The Rockwell HGS doesn't need enhanced or synthetic vision for takeoffs as low as 300' RVR on approved runways. With suitable runway lights, even the HGS isn't required for takeoffs as low as 500' RVR.
Clearly you'd need a takeoff alternate in either case.
You have VERY limited cues with visibility that low, but less is required to fly off of the runway than is needed to land on it, so it is approved and even somewhat routine in places like Salt Lake City and Seattle.
So what IS the takeoff guidance system, or in Rockwell vocabulary, a Head-up Guidance System? It is a HUD very much like in a fighter, with all primary flight instrumentation and guidance visible directly in front of the pilot, so the runway lights and the localizer guidance are superimposed, and the latter is visible even if a dense patch of fog obscures the former.
With enhanced vision, an IR picture from a camera mounted near the HUD is superimposed as well, and depending on the capabilities of the IR, you may never be in weather below Cat I again!
Added: Rockwell HGS promo video
Added: Rockwell Synthetic Vision video
Added: Gulfstream Enhanced Vision video


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What, exactly is "on the MEL"?
The MEL, minimum equipment list, defines whether fault of some equipment on the aircraft prevents it from being dispatched for flight or not.
However, sometimes (e.g. in comments to this question) there is misunderstanding regarding what it means to say something is on the MEL. So, when I say something is on the MEL, does it mean that:

the aircraft can't be dispatched without it, i.e. the list contains the required items, or
that the aircraft can be dispatched without it, i.e. the list contains the optional items?

This answer suggests the former, but I've heard/read it used in the other way, so I would like some clarification.

As a little background from the past, in the 1990s I flew for two different 747 carriers, both of which were known for their less than optimal maintenance, except that it was optimal from the standpoint of their bottom lines. At both airlines a little yellow sticker about 0.75 inch on each side was affixed next to cockpit items that were inop. Inop items not in the cockpit had their stickers on the aluminum maintenance lot cover. Rarely was there ever a flight for which there were no stickers. The typical flight would have half a doxen stickers as I remember. A dozen was not unheard of.

Both answers in the referenced question http://aviation.stackexchange.com/questions/12070/what-is-the-mel-minimum-equipment-list/ agree with the later, that it is a list of items that can be inop and the aircraft dispatched. They are light on details, but are in agreement with my answer here and comment on the other post. From the linked answer: "it details which equipment is allowed to be inoperative without grounding the aircraft."

The MMEL and MEL list items that can be inop while still dispatching the aircraft, it also lists any required restrictions of that system being inop.
I think FAA Policy Letter 34, which is the preamble for all MMELs, gives some of the best information:
First they set the basis of an MEL, that every system/function of the aircraft must be operation to dispatch. This restriction can be superseded by the MEL:

The following is applicable for authorized certificate holders operating under  Title 14 Code of Federal Regulations (14 CFR) Parts 121, 125, 129, 135:  14 CFR  require that all equipment installed on an aircraft in compliance with the Airworthiness Standards and the Operating Rules must be operative. However, the Rules also permit the publication of a Minimum Equipment List (MEL) where compliance with certain equipment requirements is not necessary in the interests of safety under all operating conditions.

Then they tell you that MEL includes items that are allowed to be inoperative along with any limitations:

The FAA approved MMEL includes those items of equipment related to airworthiness and operating regulations and other items of equipment which the Administrator finds may be inoperative and yet maintain an acceptable level of safety by appropriate conditions and limitations
The individual operator's MEL, when approved and authorized, permits
  operation of the aircraft with inoperative equipment. Equipment not required by the operation being conducted and equipment in excess of  14 CFR requirements are included in the MEL with appropriate conditions and limitations.  The MEL must not deviate from the Aircraft Flight Manual Limitations, Emergency Procedures or with Airworthiness Directives.  It is important to remember that all equipment related to the airworthiness and the operating regulations of the aircraft not listed on the MMEL must be
  operative.

The image below is from the 767 MMEL, as you can see it lists items that can be inoperative and the limitation. Some items carry many restrictions, such as anti-skid or a pack, others carry none, such as reading lights. The MMELs are available on the FAA's website, so it can be an interesting read.

I do not know why the terminology is backwards, I assume it comes from a time aircraft were much less complex and an list of required items was realistic. But if it only listed items that were required for flight, you could end up with hundreds of systems inop, with no direct requirement to repair them. PL-34 addresses this a little bit:

The MEL is intended to permit operation with inoperative items of equipment for a period of time until repairs can be accomplished.  It is important that repairs be accomplished at the earliest opportunity. In order to maintain an acceptable level of safety and reliability the MMEL establishes limitations on the duration of and conditions for operation with inoperative equipment.

and

Operators are responsible for exercising the necessary operational control to ensure that an acceptable level of safety is maintained. When operating with multiple inoperative items, the interrelationships between those items and the effect on aircraft operation and crew workload will be considered.

Basically the take away from this is that an operator can not issue every MEL in the book and dispatch the aircraft. For example, it may be okay to MEL one AC pack or one AC pack temp control valve, but it would not be okay to MEL one pack and the temp control valve on the other pack.

I am not sure the list of required items would be shorter. But for required items, there is not much to say: they are simply required. It is the items that can be inoperable under certain conditions that need something said about them: the conditions.

Technically, an aircraft can be dispatched with a non-MEL item inoperative; you just need a ferry permit from the FAA and can't carry any passengers (even non-revenue) or cargo.

@Sean this true, thanks for adding it. I will clarify that ferry flights are Part 91, not Part 121 or 135.

The minimum equipment list is a list that requires a letter of authorization in order to make it valid, and it contains items that may be inoperative or removed from the aircraft.
If something breaks or is removed, and it isn't on the MEL, then the flight is a no-go.
Source: §91.213   Inoperative instruments and equipment.
Authorization for Use

(a) Except as provided in paragraph (d) of this section, no person may
  take off an aircraft with inoperative instruments or equipment
  installed unless the following conditions are met:
(1) An approved Minimum Equipment List exists for that aircraft.
(2) The aircraft has within it a letter of authorization, issued by
  the FAA Flight Standards district office having jurisdiction over the
  area in which the operator is located, authorizing operation of the
  aircraft under the Minimum Equipment List. The letter of authorization
  may be obtained by written request of the airworthiness certificate
  holder. The Minimum Equipment List and the letter of authorization
  constitute a supplemental type certificate for the aircraft.

Regulations stating that the important items are not allowed to be listed on the MEL
**This suggests that it is a list of items that may be removed or inoperative.

(3) The approved Minimum Equipment List must—
(i) Be prepared in accordance with the limitations specified in
  paragraph (b) of this section; and
(ii) Provide for the operation of the aircraft with the instruments
  and equipment in an inoperable condition.
(4) The aircraft records available to the pilot must include an entry
  describing the inoperable instruments and equipment.
(5) The aircraft is operated under all applicable conditions and
  limitations contained in the Minimum Equipment List and the letter
  authorizing the use of the list.
(b) The following instruments and equipment may not be included in a
  Minimum Equipment List:
(1) Instruments and equipment that are either specifically or
  otherwise required by the airworthiness requirements under which the
  aircraft is type certificated and which are essential for safe
  operations under all operating conditions.
(2) Instruments and equipment required by an airworthiness directive
  to be in operable condition unless the airworthiness directive
  provides otherwise.
(3) Instruments and equipment required for specific operations by this
  part.

Your source part went incomplete.

How did this terminology get reversed? "Minimum equipment" implies that in order to fly the plane must have, at a minimum, all the items on this list. Somehow it means the opposite.

To a Brit, the term "minimal equipment list" would seem a better (but still rather cryptic) description of what it is than "minimum". In other words, "you can get by without this stuff if you have to, but you should really get it fixed ASAP".

@TomMcW Well,  it is the document which allows you to determine the minimum equipment required for dispatch. It just goes about it in a manner which may seem odd at first, but consider that there are often restrictions associated with inoperative equipment that need to be listed, and that they don't want to implicitly allow flight with something that was forgotten. It is important that the implications for each item being inoperative are individually considered. If it isn't listed, it's required and therefore is part of the minimum equipment!


text:
How many aircraft can airline put in hangar?
Another question talks about aircraft movement in and out of hangar.  Most hangar I see at commercial airport I see one aircraft per hangar.
This makes me wonder how many aircraft can be kept in the hangar depth-wise(ie nose-to-tail direction)? Is larger hangar common?
Note: please do not include special hangars such as those at Airbus or Boeing facility in main answer but side note about those are welcomed.

At general aviation airports it is quite common to have quite many (10+) airplanes in hangar, especially when gliders are included. Pushing them all in is kind a 3D tetris when trying to push one aircraft wing below other aircraft fuselage.
In some cases some gliders are winched up and stored suspended below the roof.

Related question: What is the minimum distance between two civil airplanes parked in a hangar?

As many as possible. The number of aircraft will vary depending on the size, (wing) height above the ground, etc. Most commercial airliners put any number of aircraft as long as there is no problem of damage during movement.
For example, the following image shows one Boeing 747 Dreamlifter (N780BA) parked between two Airbus A380’s inside Lufthansa Technik’s Fankfurt hangar.

Source: airlinereporter.com
The hangars are usually on the larger side because they are designed and constructed keeping the larger aircraft in mind. Then smaller aircraft will have little problem fitting into that. This image shows the floor plan for an aircraft hangar.

Source: psp-architekten.de

A) That image is quite odd, seeing a Boeing between the two Airbus (I wonder if it was getting picked on ;).  B) Since the OP mentioned aircraft parked nose-to-tail, while you can only get 1 A380/747 in that hanger, you could get at least 9 C172s in there with plenty of room to spare!

There are no restrictions. You can put as many aircraft into a hangar as you can fit into it.
Some commercial hangars are neatly arranged.

Some are not as neatly arranged but efficiently packed.

And sailplanes can be lifted and hung from the ceiling for more space on the ground.


text:
What limits the lifespan of helicopters?
The lifespan of aircraft is generally limited by metal fatigue. This is true for fixed wing aircraft; is it also true for helicopters? What is the determining factor for helicopter useful life?

My understanding that the lifespan of a fixed-wing aircraft depends on many factors. IIRC, metal fatigue is the primary issue for aircraft with pressurized cabins, but not necessarily for aircraft with unpressurized cabins.

Helicopters are also subject to metal fatigue and there have been accidents attributed to it but the primary determination is component life times.  All of the engine, transmission and rotor parts are lifed and most of the control mechanisms.  Depending on the helicopter, there will be many more lifed components.
Some helicopters also have fixed intervals between major overhauls by the manufacturer.  For example, the R22 is effectively rebuilt to an "as new" standard by Robinson at 2,200 hours.
Corrosion might also play a part.  There may be a time when it is just not economical to continue to repair and service the airframe.

I am a Aerospace Systems Engineer and former Royal Air Force. Although my qualifications and experience are within the avionics arena  I feel I can answer this question:
There are basically 3 types of Helicopter and for that fact any aircraft:

Military
Civil – Private
Civil – Commercial

The military aircraft have the shorter life in terms of flying hours, the Civil Commercial the longest life in terms of flying hours where as the Civil Private / light aircraft have a very long life in terms of years.
A military aircraft can have an airframe file of say 4,000 to 6,000 hours compared to some civil commercial aircraft with an airframe life of 60,000 to even a 100,000 hours.
Now that is for the airframe and ONLY the airframe.
The engines, landing gear and most important in terms of helicopters Gear Boxes, Rotor Heads & Blades all have significantly shorter life.
One example is that I used to work on the RAF Chinook HC1 i.e aircraft as originally delivered to the RAF by Boeing Vertol.
These aircraft where returned to Boeing to be up-graded to the RAF HC2 standard and where returned to the RAF as “New” “Zero Hour” airframes.
So, as I say its not always the airframe but the bits that are bolted on to it.
Now, I worked on the RAF HC1 Chinooks from 1988 to 1991.
In April 2018  I went to RAF Odiham on a photography shoot event organised by TimelineEvents.Com
During that photoshoot I saw aircraft that I had worked on whilst I was on 7 Squadron i.e this particular aircraft must originally been delivered to the RAF in about 1986 making it about 32 years old. However, I would say that the rotor blades will / must be less than 5 years old. Again, another however, the Engines (2 off) and gear box’s (5 off) will of be an indeterminate age but will / must contain a mixture of bits dating from less than 12 months old all the way through to the 32 years age of the original airframe.
I think though the most remarkable aircraft was ZA671.
It was delivered to the RAF as a HC1 Chinook and returned and rebuilt by Boeing as a HC2.
It crashed whilst in the USA sustain what the RAF calls Cat 4 damage – Cat 5 being a write off and Cat 1 being scratched paintwork.
Boeing rebuilt this aircraft as a HC3 Chinook and it’s the one I worked on and is still flying and I have to say that seeing the crash report and photos I am surprised that it was not classed as Cat 5 and I really would not have liked to fly in it during its test flight post accident repair.
But the point is that again it depends on what the aircraft is built  for, how it's used, how it's maintained, "usefulness”, it's value v. cost of next major servicing.
All of the above will totaled together determine the actual life of an aircraft

OK - a couple of comments on the Chinook again based on artices from James 360 and Flight International. The RAF is buying another 16 Chinook's. I gues these will be Mrk 7's ? Any way the on-line articles correctly point out that some of the Aircraft ar over 40 years old ! This is true. Our 1st Chinooks where built and delivered before the Falklands War which was in 1982 ! On a recent trip to RAF Odiham i say a few aircraft that i had worked on when i was there from Oct 85 to Nov 88.
There where also some newer aircrfat. However, they where all built to the Mk 3/5 stnadard and a few years ago

Nothing limits the lifespan of a helicopter.
There are many bits and pieces that need to be maintained in order for the helicopter to remain serviceable but so long as there is nothing broken on the helicopter and all overhauled items are within their overhaul limits, and all lifed items are within their life limits... keep on flying.
An Aircrane (Siskorsky S-64) I used to work on just rolled 20,000 hours total time on her fuselage.  Still going strong.
I don't know of any machine that has a hard airframe time that puts it out of service permanently.  Sorry... no Commercially manufactured helicopter... there may be a kit machine that has a limited life.

I am told that the hourly and calendar service life of many military helicopters are established by the OEM.
Under certain circumstances, that can be extended when scheduled "rework events" are accomplished by the manufacturer or a certified facility.
The military uses industrial rework facilities "depots" to ensure many fuselages remain airworthy beyond established service life.

Fatigue is a problem that limits, if not the life of the helicopter, at least the working life of some of its key elements, in particular of those subject to strong vibration and made from materials (such as aluminum alloys) that have a fatigue limit.
Vibration is the main culprit, and it usually comes from the rotors. In rotary-wing aircraft, vibration can be contained, but never fully eliminated.

Most helicopters will go though some sort of "Phase" of "Depot" inspections where different components will be replaced due to life-span requirements. For example; a uh-60L will require a shock strut replacement every 1500 flight hours to prevent a collapse of the strut due to over use.


text:
How to escape from an aircraft if the door is not armed?
Following the question about arming the door, the link states that doors are usually armed before engine start. What if something goes wrong when passengers are already boading with doors un-armed how to escape from the airplane?

The door the passengers are loading through is obviously one route, back down the jetway or stairs.
The door being "armed" does not affect whether it can be opened or not.  When the door is armed, opening it will also automatically inflate the escape slide.  When the door is disarmed, the slide will not inflate.
Additionally, each door has a manual inflation handle for the escape slide which the crew can use to deploy the slide if needed.
I could not find a non-copyrighted picture to include.

It's fine to use a copyrighted image for educational purposes. It's called "fair use".

Not every picture though, even fair-use has limitations. But thats a discussion for the META site  @ColeJohnson

Cockpits also have escape ropes.

If the passengers are boarding, the stairway or jetway will still be in place, so this would still be the main route to evacuate the aircraft. There is no requirement for the door to be armed and for the slides to be triggered during an evacuation while the aircraft is still "docked".
If there is an emergency onboard after the stairway or jetway has been removed, but the door not having been armed yet, the evacuation slides can be trigged manually if they are needed.


text:
Is it permitted to load a full cargo container onto an aircraft without a roller track loading/locking system?
Aircraft with roller track cargo loading systems transport containers/pallets in the cargo compartments. When an aircraft doesn't consist of a certain system but just a flat floor (so for example a small bulk cargo aircraft), is it allowed (regulation wise), and if the dimensions are no problem, to place one or more (loaded) containers in the aircraft?

Welcome to aviation.SE! I don't really understand your question: why would it not be allowed to put containers into an aircraft? Are you asking if a roller track system is required for all cargo aircraft? Or are you asking how a cargo aircraft is loaded if there are no rollers or other special features?

The roller systems consist of locks which secure the the containers. When you put a container in an aircraft without roller systems (and without these locks) the container will not be secured. So is it then allowed for the airline to just put a container in such aircraft and secure the containers in their own way?

It's important to mention what region you're asking about, when you ask about regulations. They can be very different between Europe, USA, China, etc.

Let's say Europe

(I just saw you asked about Europe right as I posted this, if this is not applicable any more I will remove it)
If Im reading this correctly the question is asking "how is cargo secured if not loaded through the use of a Unit Load Device (ULD)"
Here in the US under the FAA there are some guide lines for tying down cargo if no ULD is present. You can read them here (SAFO 13008) and here (SAFO 13005). Much of the over arching information can be found in this Advisory Circular On Air Cargo Operations (AC 120-85).
In short,

...The manual must state the policy and provide procedures to determine
  the intended reaction load for each tie down to ensure sufficient
  special load restraint for flight loads...

You can tie it down as long as you conform to the above linked documents and ensure the straps and tie downs are sufficient to hold the cargo.

Thank you for your anwer. But if you want to place a loaded ULD in an aircraft, without the proper locks for securing (so also without roller system), is this also allowable?
(without the question "how are you going to put the loaded container at its place?")

I actually read the question more along the lines of "may ULDs be loaded into aircraft that are not properly equipped for ULDs". But the question is unclear.

Under the FAA they dont seem to specify what the cargo is so you could tie down a ULD if need be as I read the regulations.


text:
Does a request for passengers to open vents indicate pressurization issues or equipment failure?
This occurrence was a year ago, but it kept bugging me until this day. I am a frequent flyer and this happened only this one time. While the plane (a Swiss A320) was still by the gate and the boarding just completed, the attendants asked the passengers to open the overhead vents because (not sure about the exact term) they have cooling difficulties. At that point it sounded reasonable, but it was around 09:00 in the morning and it wasn't a particularly warm day, it was 20°C at most outside (history says that the maximum temperature that day was 25°C). Roll-back and lift off were briefly after the boarding was complete.
Does a request like that indicate a failure or pressurization issue? I believe we were safe, just curious.

Sounds to me like they needed a system to move air around to stay at the proper temperature. Probably nothing to do with pressurization or any failures.

A fully loaded A320 holds between 150 and 195 people. Each person puts out around 330 BTU's. Taking the lesser number that means that there is about 50,000 BTU's of heat generated by the passenger load. Maybe one of the air conditioning packs was down, or they were running on ground power, its hard to say, but even on cool days an aircraft can heat up pretty quick just from the passengers.

Only British pax put out BTU's. With most other nationalities one has to keep up with (a lot more) joules.

@RobVermeulen Americans also use BTUs for purposes of HVAC systems.

I think it was a joke...Split system ACs are also ranked by BTU, and where I'm from we use cyrilic most of the time :D

No offense intended...It just made me think about once being told that in Spitfires fuel flow was indicated in dozens of pounds avoirdupois per fortnight.

@RobVermeulen British passengers put out Watts/Joules too. These days only American passengers put out BTU's (per hour!) What bothers me most is that Americans insist on referring to the US gallon as an "English" unit. The English gallon is better, because it is bigger, but we've been buying our petrol in litres for over 30 years now.

@LevelRiverSt The US gallon was derived from the 1707 English wine gallon so it's still sorta English, wot? Just not 'Imperial'. And liters (or litres) and miles are weird mix.

@SpehroPefhany That's why we buy petrol in litres and measure fuel consumption in miles per (imperial) gallon!

I prefer to measure my mileage in rods/hogshead, but I get weird looks from my wife, so I just refer to my weight in stone because it sounds much nicer. :D

I have occasionally asked passengers to do the same thing.
I have also asked for window shades to be lowered.
The reason is usually because the APU was not working and the ground air conditioning was not doing a good job or was unavailable.
Without the APU the aircraft's airconditioning can not work and engine starting relies on a ground air source to provide air pressure to spin the engines for start up.
When using ground air for starting, the ground air conditioning  is disconnected first and it takes very little time for the cabin to become uncomfortably warm.

I guess this is as good as an answer can get, first-hand :)

Opening the vents wouldn't do anything while the ground air conditioning is disconnected though, would it? The only thing it will do is bring the cabin back to desired temperature quicker once the engines start and start providing bleed air, yes?

Opening the vents would help with airflow and the comfort level in a warm cabin even without the air conditioning packs running.  Most passengers start reaching for them as soon as it starts to warm up in the back.

@JanHudec moving warm air is better than stagnant warm air any day of the week - that's why fans are so popular.  ;)

@MikeSowsun, that means there is another fan creating some pressure even when packs are not running. I didn't realize there was one.

The air coming out of the little gasper vents above the passengers' heads is the same air that comes out of the "normal" air vents (in the ceiling and/or below the hatracks). Therefore, while opening the air vents won't cool down the cabin any faster, the passengers will feel more comfortable because the gasper air comes out much much faster (and is blowing directly at their faces), giving a subjective sensation of cooling (through forced convection). The normal air conditioning system, on the other hand, is designed to minimise the air speed near the passengers to avoid drafts.

@JanHudec: Yes, there are recirculation fans which pull "used" air from the cabin, filter it, and blow it back into the cabin. Normally this air is mixed with fresh (outside) air from the packs, but even if the packs aren't running these fans will keep the air moving.


text:
How would you use the mental clock code to solve this dead reckoning problem?
Can someone explain the question below in details?
You plan to fly a cross country flight at 2 000 feet at a true airspeed of 120 knots. Your track is 270° (True) and the wind is from 225° (True) at 24 knots. Using the Mental Dead Reckoning Clock Code, what true heading would you steer, and what would be your magnetic heading if the local magnetic variation is 4° West?

"Mental Dead Reckoning Clock"  Not even a whizz wheel?

I'm afraid not. It's a question from the PPL theory questions book. I know how to determine the 'max drift angle' and but don't know how to include this material to find the magnetic heading.

Step 1: Calculate maximum drift.
Max drift $ = \frac{wind speed}{TAS (NM/min)} = \frac{24}{120/60} = \frac{24}{2} = 12$
That means if you have a direct crosswind, you'll need to correct 12$^{\circ}$.
Step 2: Determine how much of the wind is crosswind
The mental clock code is a way of estimating crosswind component from total wind. There are 60 minutes on a clock face.  If the wind direction is 60$^{\circ}$ or more, it's considered all crosswind, just as 60 minutes is considered the whole clock face.
By extension, a wind angle of 30$^{\circ}$ means 30 minutes, which is half a clock, so half the wind would be considered crosswind.  15 degrees would be a quarter of a clock, therefore a quarter of the wind, and so on.
Your maximum drift is 12 degrees with a full crosswind, but you don't have a full crosswind. Instead you have a 45$^{\circ}$ angle, so 45 minutes of a clock, which is $\frac{3}{4}$.
$ 12 * \frac{3}{4} = 9$ so you'll need to apply 9 degrees of crosswind correction toward the wind.  $270 - 9 = 261^{\circ}$
Step 3: Correct for variation
"East is least, West is best".  If variation is west, add to true to get magnetic.
$261 + 4 = 265^{\circ}$


text:
How would I calculate CG in this practice problem?
As I'm studying PPL theories, I've encountered with this kind of a question below and it would be great to understand the principle behind the calculation of the 'CG'
Calculated take-off mass = 2300 lbs, calculated CG = 95.75 in, fuel burn = 170 lbs on station 87.00 in.
Where is the CG situated after the landing?

Not too much theory, just simple math.  You find the spot where the sum of all moments
(mass x distance) = zero.  Where you would balance the plane on a see-saw, that's  your CG. You start out with 2300 lbs at 95.75 inches and remove 170 lbs at 87.00 inches.
First, find the difference in CG position, then remove the moment of the burned fuel.

$95.75in - 87.00in = 8.75in$

$170lb * 8.75in = 1487.5inlb$

The new weight is 2130 lbs. The new CG is located further aft, because the fuel station is fwd of the original CG (therefore, the front is lighter after burning the fuel).

$\frac{1487.5inlb}{2130lb} = 0.70in$

So new CG is at 96.45 inches.

An equivalent, but more intuitive way for my brain...
The total moment of the aircraft at gross
$2300 lb * 95.75 in = 220025 in lb$
The moment of the burned fuel (negative)
$-170 lb * 87 in = -14790 in lb$
Combine them (add)
$205435 in lb$
Divide by the final weight $2300 lb -170 lb = 2130 lb$
$205435 in lb / 2130 lb = 96.45 in$
The location of the CG after fuel burn.


text:
Why are there no magnetic compass errors during skidding turns?
Could someone break down why the magnetic compass reads accurate on all turns-to-headings, regardless of geographic position, when performing rudder-only turns with no bank?

It does not do anything of the sort. What gave you that idea?

As long as compass has any room to tilt side to side in housing it will not read correctly in a skidding turn.

Maybe a vertical card compass might?  I don't know about that one-

The only true answer would be "because the compass you are speaking of must be.a "Bohli" compass, featuring a needle in full 3-dimensional alignment with the earth's magnetic field, and immune from all turning errors."

The foundation of the myth may be that many compasses are seated on a very fine pin and rotate along the plane of the horizon.
Banking or manuvering may cause one of the ends to stick.  Also, banking moves the compass out of plane so "North" may become "up" or "down", again causing error.
But yawing can also cause the rotation to "overshoot" its proper reading and spin past it.  This is one reason to fly a rectangular or box pattern, allowing instruments (and our senses) to settle unaccelerated for a bit.
The heading indicator instrument is there to give more reliable readings while turning.  It uses a rapidly spinning gyro as its reference to directional change.
Interestingly enough, the heading indicator is subject to precession errors, and must be regularly reset with the compass in unaccelerated level flight.


text:
Do pilots of piston/prop aircraft have discretion to determine how much runway is required for an intersection departure?
For piston/prop aircraft requesting intersection departure, is it pilot discretion for the minimum amount of runway length required? Is there a takeoff calculator in conjunction with calculations?

Before you get in the aircraft, you should have calculated your take-off distance and added an "oops factor" or "inexperience factor". Once you know that you can ask the tower the TODA if you don't have it handy. Typically when I was going to ask for an intersection, I would know ahead of time which one would be my "bare minimum" as part of preflight planning.

I don't really understand the question. A determination is not "discretion." The pilot is required to look up the minimum amount of runway and make a decision to accept or refuse an intersection departure accordingly, as the other answers point out. There is no "calculator," only the question of whether the downfield runway remaining is sufficient or insufficient...

Yes, the pilot has discretion.  But it can have fatal consequences.

For the first part of your question, yes.  It is always the pilot's discretion to either request, or to refuse/accept an intersection departure if offered by the tower.
To the second part, yes as well, but "takeoff calculator' is a little unclear.  All piston prop aircraft, (really all certified aircraft) have performance charts in the Pilot's Operating Handbook, (POH).  Pilots are trained to use these to determine ground roll distance, obstacle clearance, and other takeoff related performance numbers based on weight of the aircraft, density altitude, and other parameters.  (more sophisticated aircraft have automated tools available to help with performance calculations.)
So, the decision in the first part of the question should be based on the knowledge derived from preflight planning described in the second half of my answer.

All general aviation pilots are required to know the takeoff and landing distances needed during the operation of a flight and the runway length available, per §91.103.  So to comply with safety and legal requirements, a pilot had better well know how much runway is available in an intersection departure prior to attempting it. This not only includes the distance required for a ground roll, but that needed to clear obstacles at the departure end of the runway, and offer the required accelerate-stop distance, if operating a multi-engine airplane.
The decision to accept an intersection departure is ultimately at the discretion of the pilot and the pilot is fully in the right to refuse an intersection departure and request a full length departure if they don’t feel comfortable with doing so.

Because people do have their right to privacy, few comments other than these are offered.  Nevertheless, let's think about this for a moment. An expedient action can have unintended fatal consequences. The first and last paragraphs of the introductory summary of the NTSB accident report read as follows -

The pilot and passenger departed on a local flight in the amateur-built experimental airplane using an intersection departure from the runway. Several frames of a surveillance video that captured the airplane during the initial climb from the runway showed a thin white trail of vapor/smoke behind the airplane. GPS data recovered from the airplane indicated that the airplane climbed to about 100 ft above ground level, leveled off, turned left at the end of the runway, and entered a descent. Shortly thereafter, the airplane collided with parked vehicles about 0.25 miles from the departure end of runway. Examination of the accident site indicated that the airplane impacted in a near-vertical attitude, consistent with an aerodynamic stall.

The circumstances of the accident are consistent with the pilot failing to maintain sufficient airspeed following a loss of engine power during takeoff, resulting in the airplane's wing exceeding its critical angle-of-attack and a subsequent aerodynamic stall. Instead of using the full runway length of 6,179 ft, the pilot elected an intersection takeoff with about 2,570 ft of available runway. Calculations showed that, had the pilot used the entire runway for takeoff, sufficient runway for a landing following the loss of engine power would likely have been available.


text:
Which portions of class B and C airspace does CFR 91.157 (special VFR) apply to?
CFR 91.157 says that special VFR operations may be conducted below 10,000 ft MSL "within the airspace contained by the upward extension of the lateral boundaries of the controlled airspace designated to the surface for an airport". Does the "controlled airspace designated to the surface" refer to only the center cylinder of the class B or C upside down wedding cake? Or is the language saying referring to all class B and C airspace in addition to the airspace between the surface and class B and C shelves? Thank you

We have several related questions but I am unable to find any that specifically focus on whether the Class B or C "shelves" (and also the airspace directly above or below the "shelves")  are meant to be included by the relevant language in the FAR.  Peripherally related questions include https://aviation.stackexchange.com/questions/35297/which-parts-of-class-e-airspace-can-an-ultralight-part-103-fly-in-without-prio and https://aviation.stackexchange.com/questions/35407/may-aerobatics-be-performed-over-a-controlled-airport-without-getting-a-waiver .

First question: yes.  The controlled airspace designated to the surface for an airport is the center core of class B and C airspace, class D airspace, and class E airspace all the way to the surface (innermost heavy blue, innermost heavy magenta, dashed blue, and dashed magenta lines on the VFR charts.)  This airspace, as well as any airspace directly above this airspace, is eligible for SVFR authorization, up to 10,000 ft MSL.  The other shelves are excluded from SVFR authorization - the normal airspace rules apply to those regions.  Moreover, if the center core extends above 10,000 ft MSL, that part of the center core that is above 10,000 ft MSL is also excluded.

There is a ruling from the Office of the Chief Counsel that addressed this; this answer would benefit from citing that.  Here it is: https://www.faa.gov/sites/faa.gov/files/faa_migrate/interps/2006/Hucker_2006_Legal_Interpretation.pdf .  Note that it reverses an earlier ruling that said airspace in the "shelves" was considered to be "within the lateral boundaries" of controlled airspace designated to the surface.

Actually though this answer could use some clarification.  Because the outer shelves are also depicted as heavy blue and heavy magenta lines on the VFR charts!

Just noticed something here-- note that the way the FAR is written, any airspace "within the lateral boundaries" of the controlled-to-surface portion (i.e. the inner core) of the Class B or C is eligible for Special VFR up to 10,000' MSL.  It makes no difference how high the actual ceiling of the Class B or C is.  If the ceiling is say 5000' MSL, or if the ceiling is 15,000' MSL, either way, makes no difference, all airspace above that inner surface footprint all the way up to 10,000' MSL would be eligible for SVFR.  This answer implies otherwise.

The point becomes especially relevant in the case of Class D airspace, where the ceiling of the airspace is typically relatively low- or for surface-level Class E airspace- which is another kind of airspace where SVFR is allowed "within the lateral boundaries of"- keeping in mind that you won't find a specific ceiling listed for the surface-level Class E airspace on the sectional chart. Also highly relevant to related question http://aviation.stackexchange.com/questions/35297/… -- the airspace above surface-level Class E airspace is off-limits to ultralights with no upper boundary.

@quietflyer if the airspace does not extend beyond 10,000 ft MSL, SVFR cannot be requested by the pilot of the airport since the airspace is not under the control of the airport.  As I understand SVFR, it is requested when the pilot advises that basic VFR cannot be maintained when entering into or transitioning through the surface area (typically the inner core) of the airspace.  Consequently, the implicit limit of SVFR is the uppermost limit of the airspace but never beyond 10,000 ft MSL.  For more info, see JO 7110.65Z 7-5-1

re "if the airspace does not extend beyond 10,000 ft MSL, SVFR cannot be requested by the pilot of the airpirt since the airspace is not under the control of the airport. " -- well, the pilot can certainly request!  As to whether the request could be granted in real life-- we have several current or former ATC folks on this site who might be able to speak to that.  Could be fertile ground for a good new ASE question.  My comment was only meant to address the actual wording of the FAR, not what could be granted in actual practice.  Wouldn't be the first time that the two are not aligned!

I think you actually meant to address the status of airspace that is below 10000' MSL but above the ceiling of the Class D, C, or B airspace.  Right?  But my same basic point applies.  As I understand it, the actual letter of the FAR says that aircraft in that airspace are eligible for SVFR.  It may be the case that ATC would always decline SVFR for any airspace above the ceiling of the Class D, C, or B, but I don't see that that is written into the FAR.  Again, seems like a good basis for a new ASE question.

Link to the document you mentioned-- https://www.faa.gov/air_traffic/publications/atpubs/atc_html/chap7_section_5.html -- I'm not seeing any specific statement in section 7-5-1 indicating that SVFR can not be authorized in airspace above the ceiling of (but still within the lateral boundaries of, i.e. above the surface footprint of) the Class B, C, or D "surface area" (inner core) airspace in question.

I think I've just convinced myself the other way.  Approach control can issue SVFR through FSS for non-towered Class E airports.  As such they would be able to grant the clearance up to 10,000 ft and above the ceiling of the tower-controlled airspace (typically class C and D since class B is typically up to 10,000 ft MSL anyway).  So, cannot request if from airport, but can request it from Approach (by way of FSS if necessary).

Re your comment  https://aviation.stackexchange.com/questions/98636/which-portions-of-class-b-and-c-airspace-does-cfr-91-157-special-vfr-apply-to/98640#comment274551_98640 -- it's been several days now so I took the liberty of modifying your answer to reflect this.  Feel free to undo any portion of the edit that you don't agree with.


text:
Are crosswind corrections during taildragger taxiing the same as with tricycle gear?
When doing crosswind corrections during taxiing with a tail dragger, is it the same with the tricycle gear or not?
Confused with the elevator part.

Such a counterintuitive way to instruct this  Why not state for example stick left forward etc...

Aileron use is pretty clear cut and is per the diagram. You position the aileron to push down on the into-wind wing.
Elevator is more nuanced.  If the propeller slipstream exceeds the wind velocity with a tail wind, you want to elevator up. Say you are taxing and hit soft ground and need more power to keep moving. You don't want the elevator down or you might just start nosing over, with the power, wheel resistance and down elevator together trying to lift the tail.
If you are coasting along at idle with a strong tailwind, technically yes you want the elevator down, but you have to be aware of what the various forces are doing and be ready to change the position, such as in a situation like I described above.
The thing is that any significant application of power will generally cancel out the tailwind and result in the net "headwind" from the prop's slipstream.
As a result I generally never taxi a taildragger with the elevator fully down; rather, if I think the tailwind is exceeding the propeller's slipstream so the net effect is from behind, I'll hold it at neutral . Neutral still gives you a down load with a net tailwind, since the surface is still sloping downhill, but if you judge it wrong and the actual net flow over the tail is coming from the propeller, at least it isn't trying to lift the tail.
At the extremes, if I found the plane nosing over and had to decide what to do with the elevator, if the engine was at idle and there was a very strong tailwind, then I'd apply full down elevator to see if that helps, ready to switch back if that just makes things worse.
In general, if you are taxiing prudently without going crazy on the speed, power and brakes, 90% of the time you'll be taxiing stick back, but elevator neutral is the safest position if there's a strong tailwind and you're not sure whether the air over the tail is from ahead or behind.


text:
For an airport to be designated as an IFR alternate, does it have to have a TAF?
For an airport to be designated as an IFR alternate, does it have to have a terminal aerodrome forecast at the alternate airport to confirm that the forecast 600-2 and 800-2 will be in place at the time of arrival?

Welcome to aviation.SE! I'm assuming you're asking about FAA regulations, but are you asking if a) the forecast conditions you mentioned are required, or b) what the acceptable ways are to get the forecasts (e.g. TAF)?

tl;dr You don’t need to have a TAF at the alternate and can use other sources of weather.
Keep in mind that there are two reasons that an alternate is required. First is to assure that the pilot has evaluated the weather at the destination and considered what to do if the destination is unavailable. Second is to let ATC know what the pilot intends to do if they lose communication. In the modern ATC system, with near universal radar coverage, that isn’t as much an issue as when the regulations were written.
In the US, the destination and alternates must comply with 91.169. It specifically says that there must be weather reports or weather forecasts for the airport. Normally when you flight plan you would rely on the Terminal Area Forecast to determine whether the weather one hour before and one hour after the estimated time of arrival at your destination is above the minimums. If that is not the case then an alternate is required. And again you would rely on the TAF for the forecast.
However, TAFs are not the only way to get a forecast. NOAA publishes Graphical Forecasts for Aviation and if the weather for the area is above minimums, you could use that as a means of satisfying the requirement.
Here is an example where the coastal forecast is below minimums but the airports inland will be VFR.

Or you could look at airports around the alternate and if they are above minimums, then your alternate would be as well. In the TAFs below, there are lots of airports that inland that do not have TAFs but that you can surmise that they will be VFR.

In practice, picking an airport with a TAF as an alternate is much easier. There is no requirement that you actually go to the alternate if you can’t make the destination. And with ADSB-In, you can monitor the weather while you fly, so you have a much better idea of what the weather is doing at your destination. You can divert to an alternate at any time it doesn’t look like the weather at your destination is below your personal minimums.
§91.169   IFR flight plan: Information required.

2) Appropriate weather reports or weather forecasts, or a combination
  of them, indicate the following:
(i) For aircraft other than helicopters. For at least 1 hour before
  and for 1 hour after the estimated time of arrival, the ceiling will
  be at least 2,000 feet above the airport elevation and the visibility
  will be at least 3 statute miles.
(c) IFR alternate airport weather minima. Unless otherwise authorized
  by the Administrator, no person may include an alternate airport in an
  IFR flight plan unless appropriate weather reports or weather
  forecasts, or a combination of them, indicate that, at the estimated
  time of arrival at the alternate airport, the ceiling and visibility
  at that airport will be at or above the following weather minima:
(1)
  If an instrument approach procedure has been published in part 97 of
  this chapter, or a special instrument approach procedure has been
  issued by the Administrator to the operator, for that airport, the
  following minima:
(i) For aircraft other than helicopters: The
  alternate airport minima specified in that procedure, or if none are
  specified the following standard approach minima:
(A) For a precision
  approach procedure. Ceiling 600 feet and visibility 2 statute miles.
(B) For a nonprecision approach procedure. Ceiling 800 feet and
  visibility 2 statute miles.

Very interesting, I didn't realize that "weather reports.....that indicate conditions will be" was the wording. In theory you could look at the current conditions, discover that it's severe clear for 300 miles, and launch without ever looking at a "forecast". Thanks for this!


text:
When and how might a pilot use the 1-in-60 rule and the 10 degree drift rule for off track error corrections?
Okay, this is a 3 part question.

How would you use the 1 in 60 rule, in the air - in flight?
When would you use the 10° drift line way and when would you use the 1 in 60 rule way?
With reference to nav. flights, am I right in thinking that when you go on nav. flights, you can go with your map, so you can literally just look down at your (maybe folded) map and see the 10° lines drawn in?

(I'm specifically mentioning the 10° lines because there may be some follow up questions on that)

I was taught the 10 degree drift line method and was encouraged not to fly by the chart. Rather, the method was to select your heading at a waypoint and fly for a reasonable amount of time, then review the chart.
Obviously it requires some features and judgement, but you'd then take out the chart and make a determination using the 10 degree lines as a guide. You can then use the double track error method to get back to your intended course.

Can you help me? I haven't flown a single nav. flight so I'm trying to get a better understanding of the world of navigation. And I wont lie, I'm struggling. It's like I have the information, but it's jumbled up, or I don't understand it fully, or something.

With reference to going off track during flight - to regain track or go straight to the destination - HOW would I execute the 10° line method and the 1 in 60 rule in the cockpit? And WHEN would I execute which one?


text:
Help in understanding this velocity triangle of a propeller

I was reading a research paper and have had difficulty understanding something. How did the author get tan(phi) in these terms?
This is something I've been trying to figure out for a long time now.

This is a question about Trigonometry, not Aviation,

Yeah exactly. But by basic trigonometry this relationship can't be obtained. I figured it has to do something with velocity triangle of propeller wing so posted here!

V_propeller, V2, and tan(phi) are related as a basic trig problem. What else are you looking for?

There is an obvious error in this paper. Just look at the final formula, and remember that for small angles $\tan(\phi) \sim \phi$. The formula says that if you increase $\phi$, $v_2$ decreases. Of course, the opposite happens.
By (trigonometric) definition,
$$\tan(\phi) = \frac{v_2}{v_{propeller}}$$
Therefore,
$$v_2 = v_{propeller} \cdot \tan(\phi)$$
The rest follows; the result is similar but you have multiplication instead of the fraction.
P.S. You can get a hint that this is a low quality paper by the fact that they obliviously confuse upper- and lowercase $v$ (on the picture and in the formulae). In math/science, case matters! Sometimes even the script matters.

Thanks for the answer. I got this from the paper DESIGN AND DEVELOPMENT OF A HYBRID DRONE by British Columbia Institute of technology. They had various professors with PhD's working on it so I thought they wouldn't have made such a basic mistake! Can you look up their report once?